Stability of a secondary-type crude petroleum recovery system



H ROOM Sept. 16, 1969 w, GQGARTY ET AL 3,467,187

STABILITY OF A SECONDARY-TYPE CRUDE PETROLEUM RECOVERY SYSTEM FiledSept. 15, 1967 I GRAOED MOBILITY ZONE 'GRADED MOBILITY ZONE p v f F%FIG. 1 OF g s sg ag ag zg lg B 34$5 2$|$ O+FW MOBILITY BUFFERDISPLACEMENT sLus 1 GRADED MOBILITY ZONE P F I DF g B 5 4 2 B is O+FWMOBILITY BUFFER DISPLACEMENT SLUG I GRADED MOBILITY ZONE P r w DFBQBQB4EB3BEB|S O'I-FW MOBILITY BUFFER DISPLACEMENT SLUG FIG.4

RELATIVE MOBILITY //v VENTORS W/LL/AM B. GOG/JRTY ROBERT 6. JONES ATTOR/VEY United States Patent O 3,467,187 STABILITY OF A SECONDARY-TYPECRUDE PETROLEUM RECOVERY SYSTEM William B. Gogarty, Littleton, Colo.,and Robert G. Jones,

Findlay, Ohio, assignors to Marathon Oil Company, Findlay, Ohio, acorporation of Ohio Filed Sept. 13, 1967, Ser. No. 667,528

Int. Cl. E21]: 43/22 US. Cl. 166-273 21 Claims ABSTRACT OF THEDISCLOSURE A process for improving the stability of a crude petroleu-mrecovery process wherein crlde petroleum is displaced from asubterranean formation by a displacement slug, a mobility buffer, andfinally a drive fluid, the improvement being that the mobilities withinat least a portion of the mobility buffer and optionally a portion ofthe displacement slug from the crude petroleum to the drive fluid aredefined with distance by a semi-logarithmic straight-line function.

BACKGROUND OF THE INVENTION United States Patent No. 3,261,399 to Coppelteaches an efficient oil recovery process wherein a subterraneanformation is flooded with an emulsion displaced by a material having aviscosity reduced gradually from that of the emulsion to that of asubsequent water drive.

In the design of a crude petroleum recovery process wherein artificialmeans (i.e. other than natural displacement) are used to displace thepetroleum from the formation, the mobilities of the displacing materialare usually increased from a low at the displacement material and crudepetroleum interface to a high at the displacement material and drivefluid juncture. Mobility is defined as the ratio of the effectivepermeability to the particular liquid within the formation divided bythe viscosity of the particular liquid. The mobility ratio betweenadjacent fluids is, of course (the ratio of their respective mobilitiesas defined herein. In a miscible system, eg, hydrocarbon displacinghydrocarbon, the effective permeabilities are identical and thus themobility ratio is equal to the reciprocal of the respective viscosities.The mobility ratios between adjoining fluids, defined as the mobility ofthe displaced fluid divided by the mobility of the displacing fluid,dictate the relative stability of the process, i.e. as the mobilityratio decreases from 1 the degree of instability of the systemincreases. For example, a mobility ratio of 0.9 indicates a more stablecondition than does 0.09.

A practical example of an unstable secondary recovery process is if themobilities of the displacement material or a portion thereof areincreased from front to back and defined with distance by astraight-line functiondisplacement at the front portion of the gradedmobility zone will be more unstable than the back portion of the gradedmobility zone. I

Also, if the mobilities of the displacement material are based onviscosities of equal increments of the material being defined Withdistance by a straight-line function from a high at the crude petroleuminterface to a low at the drive fluid, displacement at the back portionof the displacement material will be more unstable than the frontportion. This can be illustrated, for example, by grading thedisplacement material from a high of 101 cps. by nine equal incrementseach decreased in viscosity by cps. to a low of 1 cp. at the drivefluid. Assuming the process is a miscible displacement wherein thepermeabilities are the same, the relative mobility will 3,467,187Patented Sept. 16, 1969 "ice then be proportional to the reciprocal ofthe viscosity. Thus, the mobility ratio between the front portion of thedisplacement material and the crude petroleum will be 1/ 101+1/ 91, or0.89, whereas the mobility ratio between the back portion of thedisplacement material and the drive water Will be l/l1+l/1, or 0.091.Thus, the mo bility ratio at the rear of the displacement material willbe 0.091-:-0.89 or about l/lO of that at the front of the displacementmaterial indicating a much more unfavorable stability.

Applicants have discovered that by grading increasingly the mobilitiesin at least a portion of the mobility buffer and optionally a portion ofthe displacement slug from the crude petroleum to the drive fluid withdistance by a semi-logarithmic straight-line function, that such asystem will have a built-in stability and will be more stable thansimilar systems described above. By this method, the mobility ratiosbetween increments of the graded zone will be equal. As a result, thissystem will suppress the fingering effect of crude petroleum recoveryprocesses.

DESCRIPTION OF THE DRAWING FIGURE 1 is representative of a secondary ortertiary recovery process wherein O (crude oil) and FW (formation water)are displaced through a formation by S (front portion of a displacementslug) and S 8 (portions of the displacement slug having mobilitiesgraded increasingly with distance by a semi-logarithmic straightlinefunction). B is part of the mobility buffer and has a mobility equal tothe back portion of S B B are the rest of the mobility buffer and theirmobilities are graded increasingly with distance by a semi-logarithmicstraightline function. Preferably, the mobility ratios between B and Band between B and DF (drive fluid) are equal. Sufficient amounts of DFare injected into I (injection means) to displace the displacement slugand mobility buffer towards P (production means) and crude petroleum isrecovered from P.

FIGURE 2 represents a preferred embodiment of the invention wherein S, Band B B (portions of the mobility buffer having mobilities gradedincreasingly with distance by a semi-logarithmic straight-line function)are displaced through the formation by suflicient amounts of DE.Preferably, the mobility ratios between B and B and between B and thefront portion of DF are equal.

FIGURE 3 is also an embodiment of the invention wherein O and FW aredisplaced towards P by S followed by B B (having mobilities graded withdistance by a semi-logarithmic straight-line function) and suflicientamounts of DE injected into I to effect the displacement. Preferably,the mobility ratios between S and B and between B and the front portionof DF are equal.

FIGURE 4 is a semi-logarithmic graph which illustrates the relativemobilities of the B -B fluids within the graded mobility buffer zone ofFIGURE 3. The B' B' letters represent mobility values for eachparticular portion of the graded mobility buffer zone. The horizontallines on the graph are representative of the particular B portions ofthe mobility buffer. As the graph illustrates, the mobility ratiosbetween each portion of the mobility buffer including the ratios betweenthe back portion of S and 3' and between the front portion of DF and B'are all equal.

It is to be understood that the number of B portions and the number of Sportions are relative and these numbers can be increased or decreased.

DESCRIPTION OF THE INVENTION The displacement slug can be any materialwhich will effectively displace all, a major portion, or an economicallyattractive portion of the crude oil and/or formation water. Examples ofsuch slugs include liquefied petroleum gases (herein defined as LPG),alcohols (e.g. isopropanol, tertiary butanol, and the amyl' alcohols),aldehydes, ketones, esters, Water and oil-external emulsions, water andoil-external micellar solutions, and any like fluid. These slugs can beclassified as miscible (i.e., they reduce the interfacial tensionbetween the crude oil and formation water and are more phase compatiblewith the crude oil) and immiscible (i.e., these slugs do not greatlyaffect the reduction of interfacial tension as the miscible slugs andare more phase compatible with the formation water).

Examples of miscible processes include slugs such as an oil-externalmiscellar solution, isopropanol, and tertiary butanol, followed by awater-like mobility buffer. Where most of the crude oil but little ofthe formation water is displaced, the slug can be an oil-externalemulsion, LPG or an oleophilic alcohol followed by a suitable mobilitybutferalso, this system can be effected by an oilexternal emulsion orLPG slug followed by LPG as the mobility buffer with natural gas as thedrive fluid. Where desirable, the slugs may contain agents to increasetheir vlscosities.

Examples of immicible processes are those wherein the crude oil andformation water are displaced by thickened water, water-externalemulsions or water-external micellar solutions. In this process, thedisplacement slug and the mobility buffer can be identical and utilizedto immediately displace the crude oil and formation waterhowever, adisplacement slug followed by mobility buffer can be incorporated.

Preferably, the displacement slug is a micellar solution. The termmicellar solution as used herein is meant to include microemulsion[Schulman & Montague, Annals of the Academy of Sciences, 92, pp. 366371,(1961)], oleopathic hydro-micelles [Hoar and Schulman, Nature, 152, p.102 (1943)], transparent emulsion (Blair, Jr. et al., United StatesPatent No. 2,356,205) and micellar solutions defined in United StatesPatent Nos. 3,254,714 and 3,275,075. Such micellar solutions can begenerally characterized by their equilibrium tending toward furtherdispersion or solubilization of the internal phase rather thancoalescence of this internal phase.

The micellar solution is composed essentially of a hydrocarbon (e.g.,sweet and sour crude oils, straight-run gasoline containing lowerhydrocarbon fractions equal to or greater than at least pentane andliquefied petroleum gases), an aqueous medium such as water orwater-containing bactericides, corrosion inhibitors, etc., and asurfactant suflicient to impart micellar solution characteris tics tothe mixture. Examples of useful surfactants include alkyl arylsulfonates, more commonly known in the art as petroleum sulfonates, oras alkyl aryl naphthenic sulfonates. Additional examples of surfactantsare found in United States Patent No. 3,254,714. In addition, themicellar solution can contain a co-surfactant such as a semipolarorganic compound selected from the group consisting of alcohols,ketones, esters, amides, etc. Examples of the alcohols include thosecontaining up to about 20 or more carbon atoms, e.g., isopropanol, 11-and isobutanol, the amyl alcohols, 1- and 2-hexanol, land 2-octanol andp-nonyl phenol. Electrolytes, such as inorganic acids, inorganic bases,organic bases, and inorganic and organic salts, e.g., sodium hydroxide,sodium chloride, sodium sulfate, sodium nitrate, similar alkali metalsalts, etc. can also be added to the micellar solution. Also, brine,i.e. salty water, can be substituted for the water in the micellarsolution.

As mentioned previously, the displacement slug is followed by a mobilitybuffer. The mobility buffer is a fluid having a controllable mobilityand is compatible with the displacement slug and the drive fluid. Onereason for the latter is to buffer the mobilities of the displacedmaterial (i.e. crude oil and/or formation water) from the drive fluid.Another reason is to protect the rather expensive displacement slug frominvasion by the highly IlQbile drive fluid.

The mobility buffer can be LPG, a lower molecular weight alcoholcontaining from one up to about 4 carbon atoms, a water-externalemulsion, a water-external micellar solution, a thickened water, or anyfluid acting similar to these. For displacement slugs requiring mobilitybuffers exhibiting water-like characteristics, the buffer preferably iscomposed essentially of two components, i.e., an aqueous medium such asWater, and a thickening agent. Examples of thickening agents includesugars, dextrans, carboxyl methylated cellulose, amines, polymers,glycerins, alcohols, and mixtures of these agents'; A particularlyuseful agent is a high molecular weight partially hydrolyzedpolyarylamide, e.g., the Pusher products sold by Dow Chemical Company.In addition, the mobility buffer may contain a co-surfactant and/or anelectrolyte, such as are identified above.

Where the mobility buffer is composed substantially of hydrocarbon,thickening agents such as high molecular weight polyisobutylene can beused to increase the viscosity.

As illustrated by the drawings, a portion of the displacement slug canhave graded mobilities. Preferably, the back portion of the slug isgraded. These mobilities can be graded with distance by a straight-linefunction, or preferably, by a semi-logarithmic straight-line function.

The mobility buffer following the displacement slug is characterized ashaving mobilities graded with distance by a semi-logarithmicstraight-line function. For example, a 2% graded portion is useful wherethe mobility buffer occupies a large percent pore volume. However, 5%,10% or larger percents are also useful and preferably the back portionof the mobility buffer is graded. All or a portion of the mobilitybuffer can be graded. A preferred embodiment is to have equal mobilityratios between various portions of the graded zones including the fluidscontiguous to the front and back portions of the graded mobility zones(i.e., the graded portions of the displacement slug and/ or the mobilitybuffer).

For example, from about 1% to about 15% of displacement slug can befollowed by from about 10% to about of the mobility buffer, percentsbased on pore volume. Within these ranges, up to about of thedisplacement slug can have graded mobilities and from about 2% up to ofthe mobility buffer can have graded mobilities. A more specific exampleis to have up to about 10% pore volume of a displacement slug followedby about 55% pore volume of a mobility buffer having graded mobilitieswithin about 20% of the back portion thereof.

Normally from about 1% up to about 15% of the micellar solution isuseful to effect efficient removal of the crude petroleum if suchpercentages are followed by 10% up to about 70% of the mobility buffer,the percents based on formation pore volume. More preferably, the amountof micellar solution can be within the range of from about 1% up toabout 10% formation pore vol ume if the mobility bufler occupies fromabout 20% up to about 50% formation pore volume with the last 20% of themobility buffer having graded mobilities as taught by this invention.However, the total amount of micellar solution and mobility bufferrequired will vary with the particular formation and acreage to beflooded.

The drive fluid can be natural gas, water-containing components toreduce the mobility thereof, water mixed with components to obtaincharacteristics desirable to the particular formation, or any likefluid. Preferably, the drive fluid is composed substantially of waterand can be water containing minor amounts of salts.

It is not intended that this invention be limited by the particulardisplacement slugs, mobility buffers, graded mobility zones, drivefluid, etc. Rather, it is intended that all equivalents within the broadconcept of this invention which are obvious to those skilled in the artbe included within the scope of the invention as described herein.

What is claimed is:

1. A process for the recovery of crude petroleum from permeablesubterranean formations having at least one injection means and at leastone recovery means in fluid communication with said subterraneanformation comprising injecting into the formation in the followingorder:

(1) a displacement slug,

(2) a mobility butler characterized in that at least a portion thereofhas mobilities graded increasingly from front to back with distance by asemi-logarithmic, substantially straight-line function,

(3) sufficient drive fluid to displace the displacement slug andmobility buffer toward the production means, and

recovering crude petroleum from said recovery means.

2. The process of claim 1 wherein a portion of the displacement slug ischaracterized as having mobilities graded with distance by asemi-logarithmic straight-line function.

3. The process of claim 1 wherein the displacement slug is a micellarsolution.

4. The process of claim 1 wherein the mobility buffer is comprised ofwater and a thickening agent.

5. The process of claim 1 wherein the back portion of the displacementslug is characterized as having mobilities graded with distance by asemi-logarithmic straight-line function.

6. The process of claim 1 wherein substantially all of the mobilitybuffer is characterized as having mobilities graded with distance by asemi-logarithmic straight-line function.

7. The process of claim 1 wherein the mobility of the back portion ofthe mobility buffer is about equal to the mobility of the front portionof the drive fluid.

8. A process for the recovery of crude petroleum from permeablesubterranean formations having at least one injection means and at leastone recovery means in fluid communication with said subterraneanformation comprising injecting into the formation in the followingorder:

(1) a displacement slug characterized in that a portion thereof hasmobilities graded increasingly from front to back with distance by asemi-logarithmic substantially straight-line function,

(2) a mobility buffer characterized in that at least about of the backportion has mobilities graded increasingly from front to back withdistance by a semi-logarithmic straight-line function,

(3) suflicient drive fluid to displace the displacement slug andmobility buffer toward the recovery means, and

recovering crude petroleum from said recovery means.

9. The process of claim 8 wherein the mobilities of the back portion ofthe displacement slug and the front portion of the mobility buffer areabout equal.

10. The process of claim 8 wherein the mobilities of the back portion ofthe mobility buffer and the front portion of the drive fluid are aboutequal.

11. A process for the recovery of crude petroleum from permeablesubterranean formations having at least one injection means and at leastone recovery means in fluid communication with said subterraneanformation comprising injecting into the formation in the followingorder:

(1) a displacement slug,

(2) a mobility bufler characterized in that at least about 10% of theback portion has mobilities graded increasingly from front to back withdistance by a semi-logarithmic, substantially straight-line function,

(3) sufficient drive fluid to displace the displacement slug andmobility buffer toward the recovery means, and

recovering crude petroleum from said recovery means.

12. The process of claim 11 wherein the mobilities of the back portionof the displacement slug and the front portion of the mobility bufferare about equal.

13. The process of claim 11 wherein the mobilities of the back portionof the mobility bufifer and the front portion of the drive fluid areabout equal.

14. The process of claim 11 wherein the displacement slug is a micellarsolution.

15. The process of claim 11 wherein the mobility buffer is comprised ofwater and a thickening agent.

16. The process of claim 11 wherein the drive fluid is water.

17. A process for the recovery of crude petroleum from permeablesubterranean formations having at least one injection means and at leastone recovery means in fluid communication with said subterraneanformation comprising injecting into the formation in the followingorder:

(1) a mobility buffer characterized in that at least a portion thereofhas mobilities graded increasingly from front to back with distance by asemi-logarithmic, substantially straight-line function,

(2) suflicient drive fluid to displace the mobility buffer toward theproduction means, and

recovering crude petroleum from said recovery means.

18. The process of claim 17 wherein the mobility buffer is comprised ofwater and a thickening agent.

19. The process of claim 17 wherein the mobilities of the crudepetroleum in the formation and the front portion of the mobility bufferare about equal.

20. The process of claim 17 wherein the mobilities of the back portionof the mobility buffer and the front portion of the drive fluid areabout equal.

21. The process of claim 17 wherein substantially all of the mobilitybuffer is graded increasingly from front to back with distance by asemi-logarithmic straight-line function.

References Cited UNITED STATES PATENTS 2,867,277 1/1959 Weinaug et al.1669 2,988,142 6/1961 Maly 1669 3,167,118 1/1965 Habermann 166-93,261,399 7/1966 Coppel 1669 3,266,570 8/1966 Gogarty 166-9 3,275,0759/1966 Gogarty et al. 1669 3,370,649 2/1968 Wogelmuth 166-9 OTHERREFERENCES Slobod et al., Use of a Graded Viscosity Zone to ReduceFingering in Miscible Phase Displacements, Producers Monthly, August1960 (pp. 12, 14-16, 18 and 19 relied on.).

STEPHEN J. NOVOSAD, Primary Examiner US. Cl. X.R. 166-275

